The heart

The heart is a muscular pump about the size of a fist, between the lungs in the chest. It has four chambers: two atria above and two ventricles below.

Activity 6.4 — a heart cut open

Get a goat's or cattle heart. Find the large vessels at its top, then cut it open and look at the chambers, the thickness of their walls and the valves.

Figure to be added

Figure — the human heart in section: right and left atria and ventricles, the valves between them, the vena cava, the pulmonary artery and veins, and the aorta.

Chamber	Receives blood from	Sends blood to
Right atrium	The body, by the vena cava	Right ventricle
Right ventricle	Right atrium	The lungs, by the pulmonary artery
Left atrium	The lungs, by the pulmonary veins	Left ventricle
Left ventricle	Left atrium	The whole body, by the aorta

The left ventricle has the thickest wall, because it pumps blood all round the body. Valves let blood flow only one way through the heart.